1. Field of the Invention
This invention relates to an electric circuit member having a thin film transistor (TFT) array and a liquid crystal display device using said electric circuit member, and more particularly to a liquid crystal display device havinga thin film transistor (TFT) array to effect switching at every picture element.
2. Description of the Prior Art
Heretofore, electric circuit members have been widely used in display devices and others. Exemplary of such devices is a liquid crystal display device. Generally, liquid crystal display devices have a structure comprising liquid crystal interposed with two substrates. On the side confronting the liquid crystal of the substrate, there are formed elements such as electrodes and others. Display is effected by controlling the state of the liquid crystal with the aid of these elements. On the surface of one substrate, an electrode is formed uniformly. On the surface of the other substrate, there are formed plural electrodes of a small block pattern (picture element) having an appropriate shape.
In recent years, there has been adopted a technique that TFT array to effect switching at every picture element is disposed on the surface of the substrate equipped with the picture element electrodes. FIG. 1 is a schematic sectional view of such a liquid crystal display device having TFT array. In FIG. 1, S and S' designate transparent substrates made of glass, etc. and 1 and 1' denote gate electrodes. 2 and 2' designate insulating layers, and 3 and 3' denote semiconductor layers. 4 and 4' designate source electrodes, and 5 and 5' denote drain electrodes. 6 is an insulating and orienting layer, and 7 is liquid crystal. 8 is a transparent electrode.
In the case where a photoconductive material is to be used for the transistor, it is desired to prevent the transistor from being irradiated with light to the utmost in order to stabilize the switching characteristics. For this purpose, there may be employed the liquid crystal display device as shown in the schematic sectional view of FIG. 2. In this device, shading layers 9 and 9' are further provided at the positions corresponding to the semiconductor layers 3 and 3' on the insulating and orienting layer 6 covering TFT in the device as shown in FIG. 1. For the shading layer, metal is generally employed.
In the devices as described above, there have been used as the insulating layer inorganic materials, for example, metal oxides such as alumina, titanium oxide, etc., silicon compounds such as silicon nitride, silicon dioxide, etc. and the like up to now. In order to cover TFT, a certain film thickness is required. However, when the film thickness of these inorganic materials is increased, there is caused a problem that cracks are liable to be generated therein with film strain which increases as the film becomes thicker. If such cracks are generated, TFT is simultaneously destroyed. Therefore, TFT is not completely protected, which degrades the characteristics thereof. Accordingly, instead of using inorganic materials, there has been proposed using organic materials in which cracks are not generated, such as silicone resins, acrylic resins, cyclized polyisoprenes, and the like for the insulating layer. However, insulating layers made of these organic materials do not have sufficient properties as required for the protecting layer and there is a defect that the characteristics of TFT become unstable.
In the liquid crystal display device as described above, the insulating layer is subjected to orienting treatment and serves for an orienting layer, too. In the case where the shading layers are formed, the orienting treatment must be carried out thereafter. By this orienting treatment, the shading layer either undergoes no orientation or becomes an orientation state differing significantly from that of the insulating layer. Tehrefore, the orientation of the liquid crystal may be disordered in the vicinity of the insulating layers, which exerts a bad influence upon the display.